Some Considerations Concerning the Photogenic Function in Marine Organisms

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SOME CONSIDERATIONS CONCERNING THE

PHOTOGENIC FUNCTION IN MARINE

ORGANISMS

F. ALEX. McDERMOTT
Washington, D. C.

In two very interesting papers, Professor C. C.
Nutting 1 has brought forth evidence tending to show that
in oceanic depths below the range of penetration of the
sun's rays, there exists a dim, phosphorescent light, quite
general in its distribution, radiated from various photo-
genic organisms of the abyssal regions, and having a defi-
nite and valuable significance for the life of animal forms
at these depths.

That such a light actually exists is scarcely to be sanely
doubted, in view of the evidence of the deep-sea explora-
tions which have added so much to the knowledge of
oceanic conditions. And that it has a purpose in the life
of the forms inhabiting those portions of the ocean beds
where it exists, seems to the writer equally undeniable,
unless we accept Emerson's poetic reasoning that

" Beauty is its own excuse for being."
Just what its purpose may be in hermaphroditic, simple
forms not provided with definite organs of sight, and
indeed also in many higher forms, may, of course, still be
a legitimate subject for investigation and consideration.

Professor Nutting's remarks have been of special
interest to the writer in connection with some recent
studies made by the latter on the general subject of bio-
photogenesis, with special reference to the Lampyridae. 2

1 (a) "The Utility of Phosphorescence in Deep-sea Animals," Amer.
Nat., Vol. 3, 1899, pp. 792-799; (&) "The Theory of Abyssal Light,"
Proc. VII Gong. Zool., advance reprint, 1910.

2 Amer. Journ. Physiol., 1910. Vol. 27, pp. 122-151; Canad. Entomol.,
1910, Vol. 42, pp. 357-363; Popular Sci. Monthly, 1910, Vol. 77, pp. 114-
121.

118

No. 530] THE PHOTOGENIC FUNCTION 119

The coloring and photogenicity of the organisms found
in the depths of the sea show some similarities to the
corresponding feakires of life on land.

Take the family Buprestida?, of the genus Coleoptera,
of the order of insects. The insects of this family are
probably the most brilliantly colored of any of the beetles,
and are colored quite as' brilliantly as the insects of any
other genus. The colors cover a quite wide range of
metallic, polished, glistening greens, blues, reds, coppery
and golden ; many of the smaller species wear more
somber dark blues, browns and blacks, but as a class they
are brilliant and showy. Obviously, these colors would
be invisible in the absence of light, and need a light of
considerable intensity to bring out their full value. Now
we find that almost without exception these Coleoptera
are diurnal; they attain their maximum activity during
the brightest daylight, and fly but little at night. But one
species has been reported to be luminous, and unless this
report is pretty definitely confirmed there is grave reason
to doubt its authenticity.

Now let us consider the Lampyridse : The beetles of this
family of almost eleven hundred species are in the great
majority of instances, luminous ; the non-luminous species
form a decided minority of the true Lampyridse. They
are also, in the great majority of cases, mainly nocturnal
in habit, hiding out of the sunlight during the day ; those
species which are markedly diurnal in habit are also those
which are non-luminous, or in which the luminosity is
relatively slight. In coloration, they show none of the
bright metallic, showy colors of the Buprestidse; black,
gray, brown and yellow-brown predominate, with occa-
sional red markings, yellow stripes and indistinct lines
and spots. In them, the photogenic function possesses at
least two definite significances: (1) it is an adjunct of the
sexual organism of the insect, rendered of value to them
by reason of their nocturnal habits, and (2) it has a pro-
tective value. In the larvae it might also be considered
to have an aggressive value, in attracting the snails, etc..

120 THE AMERICAN NATURALIST [Vol. XLV

on which they feed, but this argument would not hold for
the imagos, which are much more active.

Most of the above statements apply with equal force
to the Pyrophorini, the luminous Elateridse of the tropics ;
these insects are herbivorous, however, and the aggres-
sive significance does not hold for them.

It would seem, then, very probable that similar condi-
tions obtain in the abyssal region, with its dim weird,
phosphorescent light. The light produced by the Lam-
pyriche has recently been shown by Ives and Coblentz 3 to
have the extremely high radiant efficiency of 96.5 per
cent., against 4 per cent, for the best artificial illuminant.
The spectrum of this light is a continuous band extending
from the upper red to the lower blue with a maximum
intensity in the yellow-green. This spectrum is of wider
range than that of the sea-forms cited by Nutting, 4 but
can hardly be of less efficiency. The light of the Lam-
pyriche is generally stated to be yellow, or greenish ; there
are some slight variations among different species, but in
the main the lights are similar ; it seems that a great many
of the marine organisms also give a light of similar
tone. Therefore colors whose wave-lengths are within
the limits of those of the emitted lights of these forms,
would be distinguishable in such a biophotogenic light.
Although we do not yet know the full details of the
process of the production of light by living forms, it is
not too much to assume that Nature has developed it to
a point very near to the maximum possible efficiency, and
if such is the case, the luminous oceanic forms could emit
a very penetrating illuminating radiation with very little
expenditure of energy, and though this light might not be
of any considerable intensity, as judged by our eyes, it
could undoubtedly serve as quite a useful light to the
large-eyed denizens of the deep.

The photogenicity of Salpa, Noctiluca and other such
simple forms, which are without definite organs of sight,

3 Bulletin of the IT. S. Bureau of Standards, 1910, Vol. 6, pp. 321-336.

4 Supra 6, page 10.

No. 530] THE PHOTOGENIC FUNCTION 121

presents other difficulties. It is not, however, necessary
to the faculty of perception of light that definite organs
should exist. It is a quite well-known fact that certain
worms, bacteria, and other low organisms are able to
detect ultra-violet rays to which the human organism is
wholly without sensible response, and yet these actino-
tropic (if a coined word may be pardoned) forms show
no definite organs such as might be adapted to the receiv-
ing and recording of the very short wave-lengths of ultra-
violet light. If, then, existing organisms are known to be
affected by ultra-violet rays for which they have no
special sense-organs, it is certainly logical to assume that
they and other forms may also be susceptible to the
longer and more easily discerned wave-lengths of visible
light — especially when those wave-lengths comprise
mainly the rays possessing the highest illuminating effect
— and without the necessity for the existence of "eyes"
or other definite light-receiving organs. As a matter of
fact Noctiluca, and , numerous other marine organisms
have been shown to be susceptible to light, although
they possess no specific organs for this function so far as
we have been able to make out.

Another consideration as to the purpose of the light
presents itself here. We must consider the nature of the
medium in which these creatures live. Water does not
lend itself as readily as does air to the diffusion of the
particles which produce the sensation of smell ; and hence
while odors, or speaking more properly, from the stand-
point of marine organisms, flavors or tastes undoiibtedly
exist in the ocean water, they could not, on account of the
water currents, lack of diffusion, etc., serve the purpose
which the odors of land animals serve of giving indication
of the presence and location of the creatures. It there-
fore would not be unreasonable to assume that in the gre-
garious simple luminous marine forms, the photogenic
function takes the place to some extent of the animal
odors of land forms.

To sum up, then:

122 THE AMEBIC AN NATURALIST [Vol. XLV

From analogy to terrestrial forms, the photogenicity
and coloration of marine organisms must play some
essential part in their life histories;

The absence of definite organs for the reception of the
radiations of light may not necessarily indicate that the
forms from which they are absent are insensible to these
radiations ;

The photogenic function in certain simple marine
forms may replace the olfactory function of terrestrial
forms, to some extent.